The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
Electro-hydraulic pressure control devices (for example, a Variable Bleed Solenoid (VBS) or related device) are used to control automotive automatic transmissions and other systems. These electro-hydraulic pressure devices provide an output pressure that is a function of an electrical input. The electrical input is typically controlled and provided by a microprocessor based controller. The output pressure in turn is used to control components within the transmission. For example, a typical automatic transmission includes a plurality of actuatable friction devices, such as clutches or brakes that are controlled by an electronic control system. The electronic control system must provide the desired clutch pressure as prompted by an electrical input signal in order to achieve acceptable shift quality. Variations or inaccuracies in the output pressure supplied by the electro-hydraulic pressure device can decrease the shift quality of the transmission. Electro-hydraulic pressure device manufacturers have struggled to minimize these variations and inaccuracies.
One solution to variations and inaccuracies in the actual output pressure supplied by the electro-hydraulic pressure device is to adjust or calibrate the device in a final production test phase. However, known methods of calibrating the electro-hydraulic pressure device adjustment the curve that defines the relationship between input current and output pressure along the electrical input axis and does not significantly alter the overall curve shape or slope. While this adjustment is very helpful, it often is unable to prevent high electro-hydraulic pressure device reject rates at the supplier and does not address variation between individual devices in curve slope over the operating range.
Accordingly, there is a need in the art for a method of automatically calibrating a electro-hydraulic pressure device that improves on the accuracy of the calibration process. Additionally, this method should not require additional hardware components.